Septicaemia and meningitis caused by Neisseria meningitidis remain a global health problem, especially in young children. Neisseria meningitidis is usually a commensal of the nasopharynx, the only major natural reservoir of this organism. The virulence factors that potentiate the capacity of Neisseria meningitidis to cause invasive disease include capsular polysaccharides, pili (fimbrae) or outer membrane proteins and lipopolysaccharides (DeVoe, I. W. 1982. Microbiol. Rev. 46: 162-190; Jennings, H. J. 1989. Contrib. Microbiol. Immunol. 10: 151-165; Tonjum, T., and M. Koomey. 1997. Gene 192: 155-163; Nassif, X., et al., 1997. Gene 192: 149-153; Poolman, J. T. 1996. Adv. Exp. Med. Biol. 397: 73-33; Verheul, A. F., et al., 1993. Microbiol. Rev. 57: 34-49; Preston, A, et al., 1996 Crit. Rev. Microbiol. 22: 139-180).
Existing licensed vaccines against capsular serogroups A, C, W and X are available (Frasch, C. E. 1989. Clin. Microbiol. Rev. 2 Suppl: S134-138; Herbert, M. A., et al., 1995. Commun. Dis. Reg. CDR Rev. 5: R130-135; Rosenstein, N., et al., 1998. J.A.M.A. 279: 435-439), but generally lack satisfactory immunogenicity in very young children and do not induce long lasting protective immunity (Peltola, H., et al., 1977. New Engl. J. Med. 297: 686-691; Peltola, H., et al., 1985. Pediatrics 76: 91-96; Reingold, A. L., et al., 1985. Lancet II: 114-118; Lepow, M. L., et al., 1986. J. Infect. Dis. 154: 1033-1036; Cadoz, M. 1998. Vaccine 16: 1391-1395). Nonetheless, their utility has been significant in affording protection to selected populations such as the military, travelers and those at exceptional risk in outbreaks or epidemics (CDC. 1990. MMWR Morb. Mortal. Wkly. Rep. 39, No. 42: 763). Very recently, meningococcal conjugate Group C vaccines have been introduced as a routine immunization in the United Kingdom.
The major public health priority concerning invasive meningococcal infections is to identify Group B vaccines that are highly effective in infants and give long term protection. Group B strains have accounted for a substantial, often a majority of invasive Neisseria meningitidis infections in many countries in Europe and North America (CDR. 1997 April. Communicable Disease Weekly Report. 7, No. 14). Prevention of Group B invasive disease represents a particularly difficult challenge in vaccine development as the capsular polysaccharide is very poorly immunogenic and even conjugates have shown disappointing immunogenicity (Jennings, H. J., and H. C. Lugowski. 1981. J. Immunology 127: 1011-1018). Further, there are concerns about the safety of vaccines whose rationale is to induce antibodies to the Group B polysaccharide, a homopolymer of α-linked 2-8 neuraminic acid. The identical polysialicacid (PSA) is a post translational modification of a glycoprotein present on human cells, especially neurons, the latter is referred to as neural cell adhesion molecule (N-CAM) (Finne, J., et al., 1983. Lancet 2: 355-357). Both theoretical and experimental evidence have been used to argue that the induction of antibodies might result in autoimmune, pathological damage to host tissues.
Alternative approaches to develop vaccine candidates against Group B Neisseria meningitidis are being actively explored. These include: outer membrane porins (Poolman, J. T., et al., 1995. Meningococcal disease, p. 21-34K. Cartwright (ed.). John Wiley and sons, Wetzler, L. M. 1994. Ann. N.Y. Acad. Sci. 730: 367-370; Rosenquist E., et al., 1995. Infect. Immun. 63:4642-4652; Zollinger, W. D., et al., 1997. Infect. Immun. 65: 1053-1060), transferrin binding proteins (Al'Aldeen, A. A., and K. A. Cartwright. 1996. J. Infect. 33: 153-157) and lipopolysaccharides (Verheul, A. F., et al., 1993. Infect. Immun. 61: 187-196; Jennings, H. J., et al., 1984. Infect. Immun. 43: 407-412; Jennings, H. J., et al., 987. Antonie Van Leeuwenhoek 53: 519-522; Gu, X. X., and C. M. Tsai. 1993. Infect. Immun. 61: 1873-1880; Moxon, E. R., et al., 1998. Adv. Exp. Med. Biol. 435: 237-243).
The structure of Neisseria meningitidis LPS has been studied in considerable detail by Jennings H. and co-workers with additional contributions by others (Griffiss, J. M. et al., 1987 Infect. Immun. 55: 1792-1800; Stephens, D. S., et al., 1994. Infect. Immun. 62: 2947-2952; Apicella, M. A., et al., 1994. Methods Enzymol. 235: 242-252; Poolman, J. T. 1990. Polysaccharides and membrane vaccines, p. 57-86. in Bacterial Vaccines, A. Mizrahi (ed.)., et al. 1997. FEMS Microbiol Lett. 146: 247-253). The structures of major glycoforms for several immunotypes (L1-L9) have been published L1, L6 (Di Fabio, J. L., et al., 1990. Can. J. Chem. 68: 1029-1034; Wakarchuk, W. W., et al., 1998. Eur. J. Biochem. 254: 626-633); L3 (Pavliak, V., et al., 1993. J. Biol. Chem. 268: 14146-14152); L5 (Michon, F., et al. 1990. J. Biol. Chem. 265:7243-7247); L2 (Gamian, A., et al., 1992. J. Biol. Chem. 267: 922-925); L4, L7 (Kogan, G., et al., 1997. Carbohydr. Res. 298: 191-199): L8 (Wakarchuk, W. W., et al., 1996, J. Biol. Chem. 271,19166-19173), L9 (Jennings, H. J., et al., 1983. Carbohydr. Res. 21: 233-241). Reference is also made to the following discussion of the accompanying FIG. 1.
It is known that, in addition to this inter-strain variation, individual Neisseria meningitidis strains exhibit extensive phase variation of outer core LPS structures (reviewed in van Putten, J. P., and B. D. Robertson. 1995. Mol. Microbiol. 16: 847-853 and Andersen, S. R., et al., 1997. Microb. Pathog. 23: 139-155). The molecular mechanism of this intra strain variation involves hypermutable loci within the reading frames encoding several glycosyl transferases (Gotschlich, E. C. 1994. J. Expt. Med. 180: 2181-2190, Jennings, M. P., et al., 1995. Mol. Microbiol. 18: 729-740). Similar mechanisms of phenotypic variation have been reported for other phase-variable surface components of pathogenic Neisseria, including Opc (Sakari, J., et al., 1994. Mol. Microbiol. 13: 207-217), Opa (Stem, A., et al., 1986. Cell 47: 61-71) and PilC proteins (Jonsson, A. B., et al., 1991. EMBO. J. 10: 477-488). The high frequency, reversible molecular switching is mediated by homopolymeric tracts of cytosines or guanines through slippage-like mechanisms that results in frame shifts (Gotschlich, E. C. 1994. J. Expt. Med. 180: 2181-2190, Jennings, M. P., et al., 1995. Mol. Microbiol. 18: 729-740; Stern, A. and T. F. Meyer. 1987. Mol. Microbiol. 1: 5-12).
Despite the extensive antigenic variation of LPS, the inner core of the LPS has been considered to be relatively highly conserved, and therefore the use of the inner core of the LPS structure has been suggested for use in vaccine design. However, the problems with candidate vaccine generation in this way are numerous.
First, although it was known that certain components of the inner core could be immunogenic (Jennings, H. J. et al., 1984. Infect. Immun. 43: 407-412; Verheul, A. F., et al., 1991. Infect. Immun. 59: 3566-3573), the extent of conservation of these epitopes across the diversity of meningococcal disease isolates was not known and evidence of bactericidal activity of antibodies to these epitopes has not been shown. U.S. Pat. No. 5,705,161 discloses that oligosaccharides of meningococcal immunotypes differ, for example, with regard to monosaccharide composition, amount and location of phosphoethanolamine groups and degree of acetylation of the inner core GlcNAc unit or other units, indicating that many possible structures may be found in the core structure. U.S. Pat. No. 5,705,161 also suggests that a portion of the core of a meningococcal LPS may be suitable for use in a vaccine, although no specific immunogenic epitopes or supporting data are disclosed.
Secondly, given the presence of the outer core LPS structure and other surface exposed non-LPS structures, including capsule, it is not known whether the inner core structure is accessible to the immune system to allow a bactericidal immune response to be generated. Furthermore, any vaccine would need to contain immunogenic structures which elicit an immune response to the complete range of pathogenic Neisseria meningitidis strains. However, the extent of variation exhibited by the inner core structure of virulent strains is not known, and rigorous investigation of the problem has not been undertaken.
Furthermore, in the publication New Generation Vaccines (1997, Ed. M. M. Levine, publ. Marcel Deker Inc, New York, Chapter 34, page 481), it is stated that, with respect to vaccine development, “including LPS that consists only of the common inner core region of the oligosaccharide may not result in induction of bactericidal antibodies.”.
In addition, other species of the genus Neisseria pose global health problems. For example, Neisseria gonorrhoeae is involved in sexually transmitted diseases such as urethritis, salpingitis, cervicitis, proctitis and pharyngitis, and is a major cause of pelvic inflammatory disease in women.
Accordingly, there is still a need in the art for an effective vaccine against pathogenic Neisseria infection, such as Neisseria meningitidis and Neisseria gonorrhoeae infection.
The present invention sets out to address this need.